Capacitors are widely used in integrated circuits. Finger metal oxide metal (Fmom) capacitors are used in the current process technology (e.g., 28 nanometer (nm)). As technology scales down to 20 nm and beyond, however, variation of the thinner and slimmer metal wires used to implement Fmom capacitors becomes more and more severe, resulting in severe variation in the Fmom capacitance.
In current integrated circuit (IC) devices, a significant amount of small value (e.g., 20-30 fF) capacitors are specified. Although this was not an issue at 45 nm and older process technologies (due to a smaller variation in metal wire width/thickness (i.e., smaller capacitance variation)), starting at 28 nm, it becomes significantly more challenging to fabricate small value capacitance, while meeting design corners. Consequently, at 20 nm process technology and beyond, it will no longer be feasible to use Fmom capacitors to provide small value capacitance for IC devices.
A metal insulator metal (MIM) capacitor in the back end of line (BEOL) layers has been proposed. This solution, however, requires three additional masks as well as a high-K (HiK) oxide deposition process to achieve a high capacitor density.